There are polymerizable compositions that include, for example, a polymerizable compound having an ethylenically unsaturated bond and a photopolymerization initiator. Since such polymerizable compositions cure when exposed to light, they are used for photocurable inks, photosensitive printing plates, color filters, photoresists and the like.
In recent years, combined with the demand in various applications for polymerizable compositions having sensitivity with respect to a short wavelength light of especially 365 nm, compounds that exhibit excellent sensitivity with respect to a light source of short wavelength, for example, a photopolymerization initiator, have been increasingly desired. However, since photopolymerization initiators that exhibit excellent sensitivity are generally poor in stability, photopolymerization initiators having sufficient storage stability in addition to improved sensitivity have been demanded.
Use of oxime ester derivatives as a photopolymerization initiator in such polymerizable compositions has been proposed (see, for example, U.S. Pat. Nos. 4,255,513 and 4,590,145, Japanese Patent Application Laid-Open (JP-A) Nos. 2000-80068, 2001-233842, 2006-342166 and 2005-202252). However, since these known oxime ester compounds exhibit low absorbance with respect to light having a wavelength of 365 nm, there has been room to improve the exposure sensitivity with respect to light of this wavelength.
In view of the above, novel oxime ester derivatives, which exhibit increased absorbance with respect to short wavelength light of approximately 365 nm, improved sensitivity and favorable stability, have been proposed in recent years (see, for example, JP-A Nos. 2007-269779 and 2009-191061).
Use of polymerizable compositions utilizing these oxime ester compounds as an initiator for a colored radiation-sensitive composition that forms a colored region for a color filter has also been proposed (see, for example, JP-A No. 2005-202252). However, these compositions remain insufficient in terms of storage stability and sensitivity with respect to short wavelength light.
Use of a polymerizable composition for forming a colored region for a color filter newly creates a need to realize favorable reproducibility of color hue after the formation of a pattern, and a solution to problems such as changes in coloring property over time has been strongly desired.
There is also a strong demand for increasing the color density and reducing the thickness of color filters for image sensors for the purpose of enhancing the light-condensing capability of a solid-state image sensor such as a CCD image sensor or improving the image quality by enhancing the color-separation capability of the solid-state image sensor. In this regard, when a large amount of colorant is added to the composition in order to achieve high color density, sensitivity may not be sufficient to precisely reproduce the shape of fine pixel patterns having a size of 2.5 μm or less. As a result, there is a tendency for a lack of patterns to occur frequently in the entire region. In order to prevent the lack of patterns, the light exposure needs to be carried out with energy of a higher level. Therefore, the time for exposure may become longer and decrease in yield of products may be significant.
In consideration of the above, there is a need for polymerizable compositions used for forming a colored region of a color filter that exhibit high curing sensitivity, while containing a colorant at high concentration, in order to attain an ability of forming a favorable pattern.